1. Field of the Invention
The present invention is directed to an x-ray computed tomography apparatus, and in particular to such a tomography apparatus of the type wherein the x-ray beam is produced by an electron beam which strikes an annular anode at successive locations around the circumference of the anode to produce a rotating x-ray beam.
2. Description of the Prior Art
In computed tomography (CT), tomograms of a subject are acquired by means of x-rays that pass through the subject and are subsequently registered in a detector system while the x-ray source (or at least the x-ray focus) and the detector are moved along an arcuate path around the subject. For the presentation of moving organs (for example, the heart), the measuring time for a slice of a tomogram must lie clearly below 100 ms. Short scan times (50 ms) can be achieved with electron beam tomography (EBT).
An electron beam tomography apparatus is known wherein a ring anode is provided that is scanned by an electron beam generated by an electron gun in order to generate a rotating x-ray beam. It is thereby necessary that the electron beam intensity be the same at all positions along the ring anode, and in known systems of this type such equal intensity at all positions has either been assumed to exist, or special measures are needed to insure it.